This invention relates generally to fuel delivery systems and more particularly, to low pressure fuel injectors for gas turbine engine combustion systems.
The invention described herein was made in the course of or under a contract, or a subcontract thereunder, with the United States Department of the Air Force.
Gas turbine engine manufacturers are constantly striving for a carburetor design which will provide a fuel/air mixture to a continuous-flow combustion chamber for the achievement of complete and efficient combustion of the fuel by minimizing the occurrence of fuel-rich pockets which, upon combustion, may produce carbon or smoke. Various prior art methods have proven to be unsatisfactory for one reason or another. For example, high pressure fuel spray atomizers have not proven entirely satisfactory because of the requirements for many intricate parts including two concentric pressure atomizing nozzles and associated internal seals. Further, there is a need for high pressure fuel pumps and very small flow passages which result in high velocities and erosions. Systems for vaporizing the fuel upon injection into the combustor have also proven to be severely limited due to the dependence of the vaporization process on the temperature of the fuel and air entering the combustor.
One of the more successful alternatives for obtaining the desired performance characteristics as mentioned hereinabove, is the low pressure fuel injection system having counterrotational primary and secondary swirl vanes which efficiently atomize the fuel by the high shear forces developed at the confluence of the counterrotational airstreams. The most common counterrotational system employs, in the primary stage, an axial swirler where the air enters in an axial direction, is deflected in a somewhat circumferential direction to introduce a swirl to the airflow, and then flows axially downstream in the venturi where it finally mixes and interacts with the air from the counterrotational secondary swirler. One disadvantage of such a system is that, due to the relatively low velocity air introduced at the root of the axial swirler, a deposit of carbon is likely to be formed on the fuel injector which, in turn, may effect the flow of fuel and thereby the efficieny of the overall system. Another factor which tends to contribute to the problem is that of the high temperature condition within the area of the injector nozzle. Since the injector nozzle is in the closest vicinity of the combustion chamber, it tends to be heated up to a relatively high temperature, and when the fuel stream is discharged to the hot outer periphery of the nozzle, there is a tendency for the carbon to form on the surface thereof. Such a carbon formation may eventually build up and finally plug the injector to cause a serious malfunction of the system.
Since it is necessary to have the differential temperature between the internal fuel carrying portion of the injector nozzle and the outer structure thereof, which is necessarily exposed to the heat from the combustion zone and from the compressor discharge air, there is a problem of a differential thermal growth which tends to impose stress and may cause cracking, reduced fatigue life, and air shroud loss. Further, it is difficult to incorporate any kind of external sheet metal shield on the injector body without incurring difficulties associated with the loosening or failing of the shield structure. Finally, it must be kept in mind that since the injector structure is placed between the air supply stream and the combustor, it is desirable to minimize the air blockage and combustor penetration diameter.
Accordingly, a primary objective of this invention is to provide an improved fuel injector for introducing a fuel/air mixture into a combustion chamber for efficient and low smoke combustion of the fuel.
Another object of this invention is the provision for the delivery of fuel to the carburetor by a low pressure fuel system which does not allow the formation of carbon on the fuel injector.
Yet another object of this invention is the provision in a fuel injector nozzle for maintaining a differential temperature between the inner fuel carrying portion and the outer exposed portion thereof.
A further object of this invention is the provision for a low pressure fuel injector nozzle system which provides a minimum air blockage and combustor penetration diameter.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.